In the the previous Versions of the C# ,To check if the string is null or empty , we do it something similar to the example stated below.

if (input == null || (input  == "")
{
      Console.WriteLine("The string is Null or Empty");
}

The method string.IsNullOrEmpty in earlier versions of C# ,enables to check for the string if it is null or empty .

Eg :
if (string.IsNullOrEmpty((input ))
{
        Console.WriteLine("The string is Null or Empty");
}

The code looked much cleaner with IsNullOrEmpty  :-)

However the method doesnot work if the string contains only whitespaces.Whitespaces refers to the characters like space, line break, tab and empty string etc.
Eg :

if (string.IsNullOrEmpty(' '.ToString()))
{
          MessageBox.Show("emptyorNull");
}

The above code will return false .We have to use the Trim() method to get it to work.

if (string.IsNullOrEmpty(' '.ToString().Trim()))
{
      MessageBox.Show("emptyorNull");
}

C# 4.0 makes it easy with the new method String.IsNullOrWhiteSpace .This method finds out if the specified string contains null, empty, or consists only of white-space characters and returns the true/false accordingly .

Eg :

string input = new String(' ', 5);
if (String.IsNullOrWhiteSpace(input))
{
       MessageBox.Show("String is Empty or Null or has only White Spaces");
}

The above example will return true.

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